Sheet molding compound damper component, and methods for making and using the same

ABSTRACT

A damper component for absorbing and dissipating vibration and/or noise resonating from a device is provided. The damper component includes a viscoelastic damper layer, and a continuous constraining layer intimately contacting and encasing the damper layer. The constraining layer has a greater stiffness and higher modulus of dynamic shearing elasticity than the damper layer. The constraining layer is a molded sheet molding compound that is substantially immiscible with the viscoelastomer to provide a discrete interface between the constraining layer and the damper layer.

CROSS REFERENCE TO RELATED APPLICATION

This application relates to co-pending application entitled “Damped DiscDrive Assembly, and Method for Damping Disc Drive Assembly,” which hasbeen filed on the same date and assigned to the same assignee as thisapplication.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to damper components of the type forreducing or eliminating the resonation of vibration and/or noise, and tomethods for making and using damper components.

2. Description of the Related Art

Unsaturated polyester sheet molding compounds, also known in the art andreferred to herein as “SMCs,” have physical properties and ease ofprocessability that have made the materials popular in the production ofa wide array of goods. For example, SMCs are found in parts of householdappliances, motor vehicles, computer disk drives, and other apparatusesand devices having moving parts that generate vibration and noise. SMCare also found in generally static articles, such as in walls, siding,and doors of residential and commercial buildings and construction.

SMCs possess some capacity to absorb and dissipate vibration and noiseresonating from a proximal source. However, SMCs are sometimes deemed tolack sufficient vibration-damping and noise-damping properties forcertain situations requiring a high degree of vibration and noiseinsulation.

Viscoelastic materials are known for their ability to absorb anddissipate vibrational energy and to damp associated noise and vibration.In use, a viscoelastic material is typically applied directly to devicesthat emanate/resonate noise and vibration. The viscoelastic materialsare bonded to or otherwise operatively associated with a device as a“free layer,” that is, as a one-layer structure. Viscoelastic materialsneed not be used in isolation. For example, a substrate may be placed onone surface of a viscoelastic layer to form a composite, which may thenbe bonded to or otherwise operatively associated with a device so thatthe viscoelastic layer is bonded to or faces the structure. It is knownto incorporate viscoelastic materials in structural laminates comprisinga pair of metallic sheets (or metallic skins) sandwiching theviscoelastic material, as disclosed as an embodiment in U.S. Pat. No.6,202,462 to Hansen et al., assigned to the same assignee of thisapplication. The laminate metallic skins between which the viscoelasticmaterial is placed are known as constraining layers.

Each of the aforementioned viscoelastic materials and composites hasdrawbacks. In many of the above-described embodiments, the viscoelasticmaterial is placed in direct contact with the device to be damped. As aconsequence, the viscoelastic layer and optionally an attached substratemust be molded or otherwise shaped to match the surface contours of thedevice. However, viscoelastic layers and metallic skins generally lacksufficient moldability or malleability to allow them to be fabricatedfor and placed in continuous intimate contact withvibration/noise-resonating devices having complex shapes.

The aforementioned free viscoelastic layer and composite have additionaldrawbacks associated with their methods of use. Typically, a freeviscoelastic layer or a composite is either attached to the outersurface of the device to be damped or is installed in a housing of thedevice. In both instances, the damper constitutes an additionalstructure that otherwise would not be present, thereby imposing weightand space penalties. For example, depending upon the location of thedamper, added space must be afforded inside or outside of the device'shousing to receive the damper. Manufacturing time and costs are alsoincreased by the addition of a damper structure to a vibrating or noiseresonating device or structure.

Additionally, placement of damper layers on a device or structure maycreate design tradeoffs. For example, complex shapes are often notamenable to add-on treatments. Accordingly, parts or portions of avibrating/noise-resonating device or structure that are not or cannot beassociated with a damper layer, for example, due to the complex shape ofthe device or structure, can adversely affect dampening effectiveness.

Accordingly, it would be a significant improvement in the art to providea damper component that replaces an existing component of the dampeddevice to thereby eliminate or at least alleviate the imposed weight andspace penalties, preferably while avoiding the need for compromisingdesign tradeoffs.

3. Objects of the Invention

Accordingly, it is an object of the present invention to provide adamper component that is readily formable into a desired shape,including a complex shape, for permitting placement of the dampercomponent in intimate contact with a vibration/noise-emanating device orstructure.

It is another object of the present invention to provide a dampercomponent that may replace an existing component of a device orstructure to be damped and thereby achieve a significant improvement inthe art over known dampers.

It is another object of the present invention to provide methods formaking a damper component, including methods for making dampercomponents that achieve one or more of the above-discussed objects.

It is a further object of the present invention to provide a devicecomprising a damper component, in which the damper component replaces anexisting structure as a functional or structural component of thedevice.

It is still a further object of the present invention to provide amethod for retrofitting an existing structure or device to replace anexisting component with a damper component having a substantiallyidentical shape and/or appearance to the existing component.

SUMMARY OF THE INVENTION

To achieve one or more of the foregoing objects, and in accordance withthe purposes of the invention as embodied and broadly described in thisdocument, according to a first aspect of this invention there isprovided a damper component for absorbing and dissipating vibrationand/or noise resonating from a device, the damper component comprising adamper layer and a continuous constraining layer intimately contactingand encasing the damper layer. The damper layer comprises aviscoelastomer. The constraining layer has a greater stiffness andhigher modulus of dynamic shearing elasticity than the damper layer. Theconstraining layer is molded from a sheet molding compound that issubstantially immiscible with the viscoelastomer, thus providing adiscrete interface between the constraining layer and the damper layer.

According to a second aspect of this invention, there is provided adamper component for absorbing and dissipating vibration and/or noiseresonating from a device, the damper component comprising a fragmenteddamper layer and a continuous constraining layer. The fragmented damperlayer comprises a plurality of fragments that are noncontinuous witheach other to provide interstices between the noncontinuous fragments.The fragmented damper layer comprises a viscoelastomer. The constraininglayer intimately contacts and encases the fragmented damper layer tofill the interstices between the noncontinuous fragments. Theconstraining layer has a greater stiffness and higher modulus of dynamicshearing elasticity than the fragmented damper layer. The constraininglayer is molded from a melt-flowable matrix comprising a sheet moldingcompound that is substantially immiscible with the viscoelastomer toprovide discrete interfaces between the constraining layer and thenoncontinuous fragments.

According to a third aspect of the invention, there is provided a methodfor making a damper component for damping of noise and/or vibration. Themethod of this aspect of the invention comprises providing a damperlayer comprising a viscoelastomer, arranging at least one sheet moldingcompound sheet adjacent the damper layer to form a laminate, placing thedamper layer and the sheet molding compound sheet in a mold cavity of amold, and heating the laminate under pressure in the mold to cure (orfurther cure) the sheet molding compound sheet to form a continuousconstraining layer encasing the damper layer. The constraining layer hasa greater stiffness and higher modulus of dynamic shearing elasticitythan the damper layer. The sheet molding compound of the constraininglayer is preferably substantially immiscible with the viscoelastomer toprovide a discrete interface between the continuous constraining layerand the damper layer.

According to a fourth aspect of the invention, there is provided adevice comprising a damper component embodied by the present invention.An example of such a device is a disc drive assembly comprising a headdisc assembly and a housing. The head disc assembly comprises a dischaving a surface and a track for storage of information, a head forwriting and reading information to and from the disc, and an actuatorarm for moving the head relative to the surface of the disc. The housingcomprises a base and a cover cooperating with one another to form achamber therebetween in which at least a portion of the head discassembly is housed. The base and/or the cover is/are constructed as adamper component for damping noise and/or vibration resonated by thehead disc assembly. The damper compound comprises a damper layercomprising a viscoelastomer, and a continuous constraining layerintimately contacting and encasing the damper layer, the constraininglayer having a greater stiffness and higher modulus of dynamic shearingelasticity than the damper layer. The constraining layer is molded froma high density filler and a melt-flowable polymer matrix that isimmiscible with and not substantially chemically bonded to theviscoelastomer.

According to a fifth embodiment of the invention, there is provided amethod for retrofitting a device that resonates vibration and/or noise.The method comprises removing a structural component of the devicethrough which the vibration and/or noise resonates, and replacing thestructural component with a damper component according to an embodimentof the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are incorporated in and constitute a part ofthe specification. The drawings, together with the general descriptiongiven above and the detailed description of the preferred embodimentsand methods given below, serve to explain the principles of theinvention. In such drawings:

FIG. 1 is a cross-sectional view illustrating a damper precursorlaminate according to an embodiment of the invention;

FIG. 2 is a cross-sectional view illustrating a damper precursorlaminate according to another embodiment of the invention;

FIG. 3 is a cross-sectional view of a damper component according to apreferred embodiment of the present invention;

FIG. 4 is a cross-sectional view of a damper component according toanother preferred embodiment of the present invention;

FIG. 5 and FIG. 6 each are graphs comparing the loss factors for Example1 and Comparative Example A over a temperature range;

FIG. 7 and FIG. 8 each are graphs comparing the loss factors for Example2 and Comparative Example B over a temperature range;

FIG. 9 and FIG. 10 each are graphs comparing the loss factors forExample 3 and Comparative Example C over a temperature range;

FIG. 11 and FIG. 12 each are graphs comparing the loss factors forExample 4 and Comparative Example D over a temperature range;

FIG. 13 and FIG. 14 each are graphs comparing the loss factors forExamples 5 and 6 and Comparative Example E over a temperature range;

FIG. 15 and FIG. 16 each are graphs comparing the loss factors forExamples 7 and 8 and Comparative Example F over a temperature range;

FIG. 17 is an exploded assembled view of a conventional disc driveassembly; and

FIG. 18 is a side, elevational view partially sectioned of a computerdisc drive housing having a cover damper component according to anembodiment of the present invention, in which the cover damper componentis shown partially sectioned.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS AND PREFERRED METHODS OFTHE INVENTION

Reference will now be made in detail to the presently preferredembodiments and methods of the invention as illustrated in theaccompanying drawings, in which like reference characters designate likeor corresponding parts throughout the drawings. It should be noted,however, that the invention in its broader aspects is not limited to thespecific details, representative devices and methods, and illustrativeexamples shown and described in this section in connection with thepreferred embodiments and methods. The invention according to itsvarious aspects is particularly pointed out and distinctly claimed inthe attached claims read in view of this specification, and appropriateequivalents.

It is to be noted that, as used in the specification and the appendedclaims, the singular forms “a,” “an,” and “the” include plural referentsunless the context clearly dictates otherwise. For example, a dampercomponent comprising “a damper layer” and “a constraining layer” mayinclude one or more damper layers and one or more constraining layers,unless the context clearly dictates otherwise.

FIG. 1 is a cross-sectional view illustrating a damper precursorlaminate, that is, a laminate prior to being processed into a dampercomponent of an embodiment of the present invention. The damperprecursor laminate comprises a laminate body, generally designated byreference numeral 10. The laminate body 10 of the illustrated embodimentoptionally may be rolled into substantially cylindrical stock foraccommodating storage of the stock. The laminate body 10 comprises aviscoelastic sheet 12 interposed between a first SMC sheet 14 and asecond SMC sheet 16. As will be discussed in greater detail below, thefirst and second SMC sheets 14 and 16 are preferably in B-stage, thatis, a partially cured state, and are capable of being molded togetherunder suitable temperature and/or pressure to form a cured, continuousconstraining layer. In the illustrated embodiment of FIG. 1, theviscoelastic sheet 12 and the first and second SMC sheets 14 and 16 ofthe damper precursor laminate 10 each comprise a respective continuous,non-fragmented body at this stage in processing. The illustrated B-stagesheets are not exhaustive of the scope of the invention. For example,the sheet molding compound may be introduced into the mold cavity in anuncured or substantially uncured liquid state.

FIG. 2 is a cross-sectional view illustrating a damper precursorlaminate according to another embodiment of the invention. The damperprecursor laminate of the embodiment illustrated in FIG. 2 comprises alaminate body, generally designated by reference numeral 20. Thelaminate body 20 comprises a first viscoelastic sheet 22, a secondviscoelastic sheet 24, a first sheet molding compound (SMC) sheet 26, asecond SMC sheet 28, and a third SMC sheet 29. The first viscoelasticsheet 22 is interposed between the first and second SMC sheets 26 and28. Likewise, the second viscoelastic sheet 24 is interposed between thesecond and third SMC sheets 28 and 29 to provide alternatingviscoelastic and SMC sheets. As illustrated, the edges of each sheet 22,24, 26, 28, and 29 optionally may be exposed at the opposite ends of theprecursor laminate 20.

According to another embodiment of the invention, a damper precursorlaminate or laminate body, such as that of FIG. 1 or FIG. 2, is rolledinto a “jelly-roll” configuration, in which the layers are situated inspiral profiles. The jelly-roll is preferably yet optionally embodied asone or more SMC sheets overlaid with one or more viscoelastic sheets,preferably in a non-alternating manner. The sheets are then collectivelyrolled one or a plurality of revolutions to form the jelly-roll.Preferably, the SMC sheet defines the outermost layer of the jelly-roll.

The damper precursor laminate of the present invention is notnecessarily limited to the shapes and sheet arrangements illustrated inFIGS. 1 and 2 and the above-described jelly-roll. For example, in FIGS.1 and 2 and the above-described jelly-roll the SMC sheets alternate withthe viscoelastic sheets. It is within the scope of the present inventionto arrange a plurality of SMC sheets immediately adjacent one another(with no interposing viscoelastic sheet) or to arrange a plurality ofviscoelastic sheets immediately adjacent one another (with nointerposing SMC sheets). It is also within the scope of this inventionfor the damper precursor laminate to comprise a viscoelastic sheet orviscoelastic sheets as a surface layer of the laminate body, especiallywhen the laminate body is introduced into the mold cavity as a jellyroll. Further, the laminate body may have a different number of totalsheets than described above and illustrated in FIGS. 1 and 2. Moreover,the laminate body may include sheets of material other than the SMC andviscoelastic sheets, although the laminate body preferably consistsessentially of, and more preferably consists of, the SMC andviscoelastic sheets.

According to another embodiment, the damper precursor laminate comprisesa SMC B-stage resin sheet having the viscoelastomer or fragments thereofincorporated into the resin sheet prior to molding, that is, duringfabrication of the SMC resin sheet.

FIGS. 1 and 2 depict SMC sheets (14 and 16 in FIG. 1; 26, 28, and 29 inFIG. 2) having an identical thickness. However, the thickness of the SMCsheets may differ from one another. Similarly, although FIG. 2 depictsthe first and second viscoelastic sheets (22 and 24) having equalthickness, these sheets 22 and 24 may each have a thickness differentfrom the other. Preferably, the SMC sheets are each thicker than theviscoelastic sheets. The thickness of each layer may be determined andadjusted based on the intended application of the damper component, aswell as other factors, including, for example, the materials selectedfor the SMC and viscoelastic layers. By way of example and notnecessarily limitation, the viscoelastic sheets of an embodiment theinvention has a thickness in a range of about 0.1 mil to about 10 mil(2.54 microns to 254 microns). According to another embodiment, thethickness range of the viscoelastic sheet is about 3 mil to about 5 mil(76.2 microns to 127 microns). The SMC sheets may each have a thickness,for example, in a range of about 10 mil to about 500 mil (254 microns to1.27 cm), or about 50 mil to about 250 mil (0.127 cm to 0.635 cm),wherein a mil equals 0.001 inch. The thickness of the SMC sheets maychange during molding.

Each of the SMC sheets may be comprised of a composition that is thesame as or different from that of the other SMC sheet(s). However, formost applications it is preferred that each of the SMC sheets comprisesa substantially identical composition. Similarly, referring to theembodiment illustrated in FIG. 2, in the event the damper precursorlaminate comprises two or more viscoelastic sheets, e.g., 22/24, theviscoelastic sheets may each be comprised of a substantially identicalcomposition or may comprise different compositions from one another.

According to embodiments of the invention, the viscoelastic sheets maycomprise, consist essentially of, or consist of one or moreviscoelastomers. A viscoelastomer is stress-strain responsive. At agiven temperature, the stress-strain response of a viscoelastomer isdependent upon the strain rate. At high strain rates, a viscoelastomerwill exhibit more elastic behavior, while at low strain rates aviscoelastomer will exhibit more viscous behavior. A viscous behavior isgenerally defined as the ability of the material to significantly deformunder load and to convert the energy stored by deformation into heat. Anelastic behavior is the ability to exhibit a reversible deformationunder load. The viscoelastic layer preferably comprises, and morepreferably consists essentially of, at least one member selected fromthe group consisting of a (meth)acrylic acid based polymer and a(meth)acrylate-based polymer. As referred to herein as generally used inthe art, the term (meth)acrylic means acrylic and/or methacrylic.Similarly, the term (meth)acrylate means acrylate and/or methacrylate.By way of example and not necessarily limitation, suitable(meth)acrylate-based polymers include acrylic acid ester homopolymers.The (meth)acrylate-based polymer may also comprise copolymers orterpolymers of a plurality of different (meth)acrylic acid esters or acombination of a (meth)acrylic acid ester and one or morecopolymerizable monomer, oligomers, or prepolymers. In the case ofcopolymers and terpolymers, the (meth)acrylate-based polymer fractionmay constitute a majority (more than 50 weight percent) of the totalweight of polymer(s) in the viscoelastic material. According to anotherembodiment of the present invention, the viscoelastic layer may comprisea rubber, such as nitrile rubbers (e.g., acrylonitrile, acetonitrile),silicone rubber, fluoroelastomers, other elastomers, and combinationsthereof. A currently preferred viscoelastic material is 5-mil tape ofAvery Dennison™ UHA 1185, an acrylic adhesive available fromAveryDennison.

The choice of viscoelastic material may optionally take intoconsideration the likely operating temperature to which the dampercomponent will be subject during use. The viscoelastic materialpreferably has a glass transition temperature (T_(g)) at or below theoperating temperature of the device to be damped. The viscoelasticmaterial preferably has high damping properties near the intendedoperating temperature. Selection of the viscoelastic material may takeinto account the loss factor of the SMC and the viscoelastomer, and thedesired loss factor to be achieved. Loss factor is generally understoodin the art as the ratio of dissipated energy (or energy loss) per radiandivided by the peak potential or strain energy of a specimen. In anembodiment of the invention the loss factor (measured by ASTM E 756–98)of the viscoelastic material is greater than 0.5, and in anotherembodiment greater than 1.0, at the targeted temperatures. Theviscoelastic layer may optionally contain fillers, such as carbonnanotubes, chopped fibers (e.g., glass, carbon, aramid), inorganicparticles (e.g., silica), fly ash, etc. According to an embodiment ofthe invention, however, the viscoelastic layer optionally may besubstantially free of fillers, especially inorganic fillers such assilica.

As discussed above, the SMC sheets melt-flow about the viscoelasticdamper layer and consolidate with one another during molding toestablish the constraining layer encasing the viscoelastic damper layer.Prior to molding, the SMC sheets preferably comprise an unsaturated (orpartially saturated) polyester sheet molding compound (SMC). Theselected SMC preferably is substantially immiscible and preferably doesnot significantly chemically react with the viscoelastomer duringmolding so that, subsequent to molding, there is a discrete interface,preferably with substantially no interfacial bonding, between theconstraining layer and the viscoelastic layer. Representative SMC sheetsare available from, for example, PreMix, Inc. and Ashland Chemical. Theconstraining layer optionally also includes a filler, and morepreferably a high-density filler. The term “high density” as used hereinmeans a density greater than that of the sheet molding compound. Acurrently preferred filler comprises chopped fiberglass. Other fillersthat may be used alone, in combination with one another, or incombination with fiberglass include, for example, carbon, aramids,metal, plastics, alumina, silica, silicon, ceramics, graphite, ferrite,ferrophosphorus, bauxite, combinations thereof, and the like. Thefillers may be present as fibers, particles, powder, nanotubes (whereappropriate), granules, and the like. The fillers are preferably yetoptionally present in non-woven form, and are optionally dispersedsubstantially homogeneously throughout the constraining layer.

As discussed above, in embodiment of the invention the SMC sheets andviscoelastic layer may be arranged as a “jelly roll” or sheet stackprior to introduction into the mold cavity. Generally, sheet stackscomprise a composite of alternating layers of SMC and viscoelasticsheets laid flat. A jelly roll is similar to a sheet stack, but has beenrolled along its length or width to provide a spiral profile of sheets.A jelly roll may consist of one SMC sheet and one viscoelastic sheet,with the SMC sheet preferably constituting the outer layer.

A method for making the damper component from the precusor laminateaccording to embodiments of the present invention will be describedbelow. It is to be understood that the damper component of embodimentsof this invention is not limited to the following method, and may bemade by methods other than that described below. Likewise, thedescription below is not exhaustive and does not necessarily limit thescope of the inventive method.

Returning to FIG. 1, processing of the damper precursor laminate 10 mayoptionally comprise a consolidation step. For example, the damperprecursor laminate 10 may be passed through a cold rolling assembly ofthe type disclosed in U.S. Pat. No. 6,202,462, which is incorporatedherein by reference. Generally, the laminate 10 is in the form of anelongated, continuous web that is rolled on a supply coil, and is fedcontinuously through the cold rolling assembly. The assembly may includeone or more roller sets sufficient in number to reduce the thickness ofthe web to a desired consolidated thickness, whether said thickness isselected as prescribed in the '462 patent or otherwise. Each of theroller sets includes a pair of rollers facing one another, between whichthe web is passed in a known manner, preferably continuously. The rollersets may be arranged successively closer together to effect a gradualreduction in thickness.

The damper precursor laminate 10, optionally after having undergonethickness reduction as described above, is then charged or otherwiseintroduced into a suitable molding apparatus. At the time ofintroduction, the laminate may be in the form of, for example, a flatmulti-layer board or a jelly-roll. It is to be understood, however, thatthe charging step may alternatively comprise separately charging theviscoelastic sheet 12 and the SMC sheets 14 and 16 into the moldingapparatus as separate entities so that the laminate is first formed inthe molding apparatus. The SMC materials may be in B-stage cure state,or the SMC materials may be cured to a greater or lesser degree prior tointroduction into the mold. Examples of a molding apparatus that may beused for this embodiment of the method of the present invention includethose suitable for carrying out, for example, compression molding and/ortransfer molding. It is to be understood that other molding techniquesmay be used within the scope of aspects of this invention. It is also tobe understood that a standard, commercially available molding apparatusmay be used.

In a preferred embodiment of the present invention, the SMC sheets 14and 16 charged into the molding apparatus are in a partially curedstate, that is, the sheets are B-stage resins when introduced into themolding apparatus. An exemplary partially cured resin is an unsaturatedpolyester. The SMC sheets may optionally include curingagents/initiators to facilitate cure. Commercially available SMC sheetsoften include curing agents, such as peroxides and the like. On theother hand, the viscoelastic sheet 12 is preferably yet optionally fullyor substantially fully cured when introduced into the molding apparatus.The molding apparatus is then closed or partially closed, depending uponthe designed operation of the apparatus.

While in the molding apparatus, the laminate 10 is subject to heat andpreferably pressure. The selected temperature and pressure may vary, forexample, depending upon the SMC sheet resins selected and complexity ofthe mold shape. Generally, the temperature is greater than the melttemperature of the SMC sheet resin and preferably is high enough toinduce melt-flow and cure of the SMC sheet resins. An example of asuitable temperature range used with polyester resins is about 175° C.to about 250° C. An example of a suitable pressure range used with thesame resins is about 500 psi to about 5000 psi. Temperature and pressuremay be maintained substantially constant or may be varied duringmolding.

Preferably, the molding conditions are effective to cause the first andsecond SMC sheets 14 and 16 to melt, or partially melt and consolidatewith one another to form a continuous constraining layer 34, as bestshown in FIG. 3. The mold conditions and mold cavity size preferably areadequate to cause the first and second SMC sheets 14 and 16 to flowaround the edges and ends of the viscoelastic sheet 12 so that, uponcooling, the resulting continuous constraining layer 34 intimatelycontacts and encases the viscoelastic layer 32. In the event that aB-stage resin is selected for the sheet molding compound, moldingconditions are preferably sufficient to induce continued cure of thesheets 14 and 16. In their fully cured state, that is, when removed fromthe mold, the constraining layer 34 may be a thermoplastic or athermoset, although the constraining layer is preferably a thermoset.Although the damper component 30 is illustrated as having asubstantially rectangular cross-section, it is to be understood that theouter surfaces of the constraining layer 34 may undertake a shapedprofile, as dictated by the mold die surfaces.

In an optional embodiment, the molding process is performed underconditions effective to generate a sufficiently robust internal materialflow and mixing action within the mold for shearing the viscoelasticsheet 12 into a fragmented damper layer comprising a plurality offragments that are noncontinuous with each other. Generally, jelly rollsare more susceptible to fragmentation than stacked sheets. Withoutwishing to be bound by any theory, it is believed that during moldingjelly rolls undergo more deformation along their z-axis (i.e.,perpendicular to their surface planes) and are more greatly influencedby shearing forces than an unrolled stack of sheets.

The embodiment illustrated in FIG. 4 depicts a two-layer jelly-rollafter it has been molded into a damper component 40 in accordance withan embodiment of the method of the invention. As best shown in FIG. 4,the viscoelastic sheet has been sheared in a fragmented damper layercomprising a plurality of fragments 42 that are noncontinuous with oneanother to provide interstices, generally designated by referencenumeral 44, between the noncontinuous fragments 42. The SMC sheet orsheets are consolidated into a continuous constraining layer 46intimately contacting and encasing the fragmented damper layer fragments42 and filling the interstices 44 between the noncontinuous fragments42. As further shown in FIG. 4, the fragments 42 of the fragmenteddamper layer may possess a non-linear profile and may lie in differentplanes from one another. Generally, most and more preferably all of thefragments 42 are located between opposite surfaces 46 a and 46 b of thecontinuous constraining layer 46 and are hidden from view.

The constraining layer 46 (or 34) has a greater stiffness and modulusthan the fragmented damper layer 44 (or continuous damper layer 32),thereby providing structural support to the damper component 40 (or 30).For example, the viscoelastomer damper layer 44 (or 32) may have a shearmodulus on the order of about 1 psi to about 1000 psi, such as about 100psi. The constraining layer 46 (or 34) may optionally have a shearmodulus on the order of about 10,000 psi to about 3,000,000 psi,preferably above about 500,000 psi or above about 1,000,000. Preferably,the shear modulus (as measured by ASTM E143–02) of the constraininglayer is at least 1, more preferably at least 2 or at least 3 orders ofmagnitude greater than the shear modulus of the damper layer. Theconstraining layer preferably yet optionally has a density greater thanabout 5.0 grams/cm³ (g/cc).

In preferred embodiments of the present invention, the damper layer isprincipally responsible for absorbing and dissipating vibration and/ornoise resonating from a device. However, the constraining layer may alsocontribute to the vibration and noise-damping properties of the dampercomponent. The damper structure may comprise additional layers, bothdamping and non-damping. For example, a portion or all of the outersurface of the damper structure may include a coating. The coatingmaterial may be selected for various purposes, including aesthetics andprotection from outside forces. The coating may be applied, for example,by painting or plating (e.g., electro or electroless plating).

A non-exhaustive list of devices and articles with which the dampercomponent of embodiments of the present invention may be used fordamping the resonance of sound and/or vibration include, for example,automobile parts, computer disk drives, household appliances, consumerelectronics, power tools, industrial equipment, marine applications,sporting goods, and building components, such as walls and doors. Inpreferred embodiments of the invention, the damper component defines orreplaces a functional or structural component of the device that itdamps, such as to perform a function (other than damping) and/or tostructurally support one or more other components. In still anotherpreferred embodiment of the present invention, a retrofitting method isprovided, which comprises replacing an existing structural component ofthe device with a damper component of the present invention. The highshapeability of the sheet molding compounds of the constraining layermakes it possible to mold the damper component into various complexshapes, including a shape (and dimensions) substantially identical tothe replaced part.

For example, disc drive units are well known in the art as data storagedevices capable of storing a large amount of information generated bycomputers. FIG. 17 shows a conventional disc drive unit 100 illustratedin U.S. Pat. No. 6,529,345 and disclosed in U.S. Pat. No. 5,282,100. Thedisc drive unit includes a housing comprising a top cover mountable overand cooperating with a base 106 to establish an internal, sealedchamber. The cover comprises an inner layer 102 and an outer layer 104.Sealed inside of the chamber is a head-disc assembly comprising one ormore circular discs 108 stacked yet spaced apart from one another on aspindle motor hub, which is rotatably driven by a spindle motor (notshown). The spindle motor may be fixed to the base and/or cover of thehousing. The head-disc assembly further comprises a plurality ofread/write heads, with one head 114 provided for each disc. Theread/write head 114 transfers electronic data between the tracks on thediscs 108 and the external environment, e.g., a computer monitor orprinter. In the write mode, the head 114 writes data (input through aninput source, such as a computer key board or scanner) onto the tracksof the disc 108. In the read mode, the head 114 retrieves storedinformation from the disc tracks for relaying the information to anoutput source, such as a display monitor, printer, or other storagemedium.

Data and other information are stored over a majority of the surface ofthe rotatable disc or discs and, accordingly, are not accessible unlessthe head 114 can move sufficiently to reach a majority of the discsurface. To permit head 114 movement, the disc-head assembly furthercomprises one or more actuator arms 110 and actuator (e.g., voice coil)motors 112 for moving the head 114 radially across the disc surface to adesired location adjacent a surface or surfaces of each disc. Actuatorarms and motors may be arranged in a wide variety of designs andconfigurations known and practiced in the art. In the illustrateddevice, the actuator arms 110 turn about a pivot bearing assembly. Thepivot bearing assembly includes a stationary element such as a pivotjournal fixed to the disc drive housing at the base and cover to defineand stabilize a pivot axis. The actuator arms 110 move in response toenergizing currents sent from the motors 112, which moves the disc-headassembly on the pivot axis, swinging the actuator arms 110 to move thehead 114 radially relative to the disc 108 surface.

In conventional disc drive units, movements of the disc-head assembly,and in particular the actuator arms 110, tend to be relatively rapid andmay cause the disc-head assembly to vibrate. The vibration tends to betransferred to the disc drive housing. The cover, and in some cases thebase, of the disc drive housing commonly have a relative large surfacearea, which when vibrated, may radiate acoustic noise. In some cases,the cover may act as a speaker-like structure, producing undesirablyhigh levels of acoustic noise. Additionally, operation of the spindlemotor and rotation of the discs at high speeds (such as 7200 rpm) andairflow noise generated by the spinning discs contribute to thevibration and noise. Under some operating conditions, the acoustic noisemay be sufficient to disturb or aggravate the user.

In accordance with an embodiment of the present invention illustrated inFIG. 18, a portion of the housing, and more preferably the entire coverand/or the entire base, is a damper component. The disc drive unit ofFIG. 18 is substantially identical to that of FIG. 17, except that thecover of the disc drive unit of FIG. 17 has been replaced with a dampercomponent 50 of an embodiment of the present invention. Preferably, theentirety of the base and/or the entirety of the top cover is formed of,rather than simply lined with, the damper component. Stated differently,the damper component has a damper body extending from the internalsurface of the cover to the external surface of the cover. In oneembodiment the damper component may contribute to the hermetic seal ofthe disc drive chamber, such as by cooperating with and mounting to thebase 106. In another embodiment, the damper component may contribute tothe structural support of the disc-head assembly. In the event that boththe base and the cover comprise damping materials, the same or differentdamping materials may be used for making the base and the cover.Replacement of the base and/or the top cover with a damper component ofthe present invention is effective in damping the vibration and acousticnoises generated by movement of the actuator arms relative to the discsurfaces and the driving movement of the motor. The high moldability ofthe SMC material permits the molded damper component to possess asubstantially identical shape to a non-damper base or cover, while notoccupying excessive space.

In another preferred embodiment of the present invention, a retrofittingmethod is provided, which comprises replacing structural component of adevice, such as the cover or base of a disc drive, with the dampercomponent of the present invention. The high shapeability of theconstraining layer makes it possible to mold the damper component intovarious complex shapes, including a shape (and dimensions) matchingthose of an existing structural component of a device.

EXAMPLES

The following examples serve to explain and elucidate the principles andpractice of the present invention further. These examples are merelyillustrative, and not exhaustive as to the scope of the presentinvention.

All percentages are weight percentages, unless specifically statedotherwise. The sheet molding compounds (SMCs) for the examples andcomparative examples were obtained from Ashland Specialty Chemicals ofDublin, Ohio. The viscoelastic layer of the examples was Avery 1185obtained from Avery Dennison. The precursor laminates were molded at atool temperature of 300° F. (149° C.) at 100 psi to 400 psi for 3minutes. The molded composites were cut into 0.5 inch×10 inch beams, andwere tested with a mini hammer system. All modal tests were run fromroom temperature (70° F./21° C.) to 225° F. (107° C.) to represent awide range of operating temperatures. The laminates were compared to abaseline SMC compound laminate (comparative examples) with no dampinglayer.

Example 1 and Comparative Example A

A damper precursor laminate was prepared containing three stacked layersof Arotech® 2002 SMC containing 60 weight percent glass and oneviscoelastic layer inserted between the bottom two SMC layers. Thelaminate had charge dimensions of 8 inches×8 inches and a weight of 513grams.

The laminate of Example 1 was compared to a baseline/control laminate ofComparative Example A, which consisted of a SMC compound made from adamper precursor laminate containing three-stacked layers of SMC asdescribed above in Example 1, but with no viscoelastic damping layer.The laminate of Comparative Example A had charge dimensions of 8inches×8 inches and a weight of 511 grams.

After molding, the laminates of Example 1 (designated SMC 36) andComparative Example A (designated SMC 34, control) were subjected to tworounds of testing, and exhibited the following loss factors, which areillustrated in graphical form in FIGS. 5 and 6, respectively.

TABLE 1 (Loss Factor) for Example 1 and Comparative Example A TestingRound 1 Testing Round 2 Temperature Comparative Comparative (° F.)Example 1 Example A Example 1 Example A 70 0.017 0.0128 0.016 0.0108 1000.017 0.0128 0.015 0.0110 125 0.020 0.0134 0.018 0.0136 150 0.022 0.01640.021 0.0168 175 0.023 0.0160 0.022 0.0172 200 0.025 0.0218 0.023 0.0186225 0.027 0.0226 0.024 0.0204

The laminate of Example 1 exhibited average loss factors of 0.022 and0.020 in rounds 1 and 2, respectively, compared to average loss factorsof 0.0165 and 0.0155 for Comparative Example A. Hence, Example 1exhibited loss factor improvement of 33% and 29% over ComparativeExample A for rounds 1 and 2, respectively.

Example 2 and Comparative Example B

A damper precursor laminate was prepared containing a jelly roll f onelayer of Arotech® 2002 SMC containing 60 weight percent glass and oneviscoelastic layer adjacent the SMC layer. The laminate was rolled intoa jelly roll (with an SMC outer layer) and had a charge weight of 513grams.

The laminate of Example 2 was compared to a baseline/control laminate ofComparative Example B, which consisted of a SMC compound made from adamper precursor laminate jelly roll containing a layer of SMC asdescribed above in Example 2, but with no damping layer. The laminate ofComparative Example B had a charge weight of 510 grams.

After molding, the laminates of Example 2 (designated SMC 38, MSC) andComparative Example B (designated SMC 37, control) were subjected to tworounds of testing, and exhibited the following loss factors, which areillustrated in graphical form in FIGS. 7 and 8, respectively.

TABLE 2 (Loss Factor) for Example 2 and Comparative Example B TestingRound 1 Testing Round 2 Temperature Comparative Comparative (° F.)Example 2 Example B Example 2 Example B 70 0.0344 0.0196 0.0326 0.0122100 0.0564 0.0186 0.0448 0.0129 125 0.0766 0.0189 0.057 0.0137 1500.0824 0.0216 0.0494 0.0161 175 0.0716 0.023 0.0422 0.0172 200 0.05460.024 0.0366 0.0182 225 0.0534 0.027 0.0344 0.0192

Referring to Table 2, the laminate of Example 2 exhibited average lossfactors of 0.0612 and 0.0424 in rounds 1 and 2, respectively, comparedto average loss factors of 0.0218 and 0.0156 for Comparative Example B.Hence, Example 2 exhibited 181% and 172% loss factor improvements overComparative Example B for rounds 1 and 2, respectively.

Example 3 and Comparative Example C

A damper precursor laminate was prepared containing six stacked layersof Arotech® 2002 SMC containing 60 weight percent glass and oneviscoelastic layer inserted between the third and fourth SMC layers. Thelaminate had charge dimensions of 8 inches×8 inches and a weight of 1100gram.

The laminate of Example 3 was compared to a baseline/control laminate ofComparative Example C, which consisted of a SMC compound made from adamper precursor laminate containing six-stacked layers of SMC asdescribed above in Example 3, but with no damping layer. The laminate ofComparative Example C had charge dimensions of 8 inches×8 inches and aweight of 1100 grams.

After molding, the laminates of Example 3 (designated SMC 39, MSC) andComparative Example C (designated SMC 40, control) were subjected to tworounds of testing, and exhibited the following loss factors, which areillustrated in graphical form in FIGS. 9 and 10, respectively.

TABLE 3 (Loss Factor) for Example 3 and Comparative Example C TestingRound 1 Testing Round 2 Temperature Comparative Comparative (° F.)Example 3 Example C Example 3 Example C 70 0.073 0.015 0.052 0.011 1000.062 0.015 0.046 0.011 125 0.027 0.018 0.064 0.014 150 0.020 0.0200.030 0.017 175 0.024 0.022 0.039 0.018 200 0.031 0.023 0.031 0.021 2250.048 0.027 0.021 0.024

Referring to Table 3, the laminate of Example 3 exhibited average lossfactors of 0.041 and 0.040 in rounds 1 and 2, respectively, compared toaverage loss factors of 0.020 and 0.017 for Comparative Example C.Hence, Example 3 exhibited 105% and 135% loss factor improvements overComparative Example C for rounds 1 and 2, respectively.

Example 4 and Comparative Example D

A damper precursor laminate was prepared containing two stacked layersof Arotech® 2002 SMC containing 60 weight percent glass and oneviscoelastic layer inserted between the two SMC layers. The laminate hadcharge dimensions of 10 inches×10 inches.

The laminate of Example 4 was compared to a baseline/control laminate ofComparative Example D, which consisted of a SMC compound made from adamper precursor laminate containing two-stacked layers of SMC asdescribed above in Example 4, but with no damping layer. The laminate ofComparative Example D had charge dimensions of 10 inches×10 inches.

After molding, the laminates of Example 4 (designated SMC 41, MSC) andComparative Example D (designated SMC 42, control) were subjected to tworounds of testing, and exhibited the following loss factors, which areillustrated in graphical form in FIGS. 11 and 12, respectively.

TABLE 4 (Loss Factor) for Example 4 and Comparative Example D TestingRound 1 Testing Round 2 Temperature Comparative Comparative (° F.)Example 4 Example D Example 4 Example D 70 0.038 0.0182 0.0456 0.0141100 0.0438 0.0197 0.0906 0.0141 125 0.0812 0.0226 0.0864 0.0176 1500.162 0.0242 0.1698 0.0188 175 0.141 0.0260 0.203 0.0206 200 0.04920.0264 0.1228 0.0218 225 0.07 0.0310 0.13 0.0242

Referring to Table 4, the laminate of Example 4 exhibited average lossfactors of 0.084 and 0.12 in rounds 1 and 2, respectively, compared toaverage loss factors of 0.0240 and 0.0187 for Comparative Example D.Hence, Example 4 exhibited 250% and 542% loss factor improvements overComparative Example D for rounds 1 and 2, respectively.

Examples 5 and 6 and Comparative Example E

A damper precursor laminate designated Example 5 was prepared containingsix stacked layers of Arotech® 2002 SMC containing 60 weight percentglass and one viscoelastic layer inserted between the third and fourthSMC layers. Another damper precursor laminate designated Example 6 wasprepared containing six stacked layers of Arotech® 2002 SMC containing60 weight percent glass, and three viscoelastic layers inserted betweenthe third and the fourth SMC layers. Both laminates had chargedimensions of 3 inches×10 inches.

The laminates of Examples 5 and 6 were compared to a baseline/controllaminate of Comparative Example E, which consisted of a SMC compoundmade from a damper precursor laminate containing six-stacked layers ofSMC as described above in Examples 5 and 6, but with no dampinglayer(s). The laminate of Comparative Example E had charge dimensions of3 inches×10 inches.

After molding, the laminates of Examples 5 and 6 (designated SMC 44 andSMC 45, respectively) and Comparative Example E (designated SMC 43,control) were subjected to two rounds of testing, and exhibited thefollowing loss factors, which are illustrated in graphical form in FIGS.13 and 14, respectively.

TABLE 5 (Loss Factor) for Examples 5 & 6 and Comparative Example ETesting Round 1 Testing Round 2 Temp. Comp. Comp. (° F.) Ex. 5 Ex. 6 Ex.E Ex. 5 Ex. 6 Ex. E 70 0.015 0.071 0.016 0.012 0.092 0.010 100 0.0180.061 0.016 0.012 0.090 0.011 125 0.019 0.044 0.017 0.014 0.065 0.013150 0.021 0.037 0.020 0.016 0.048 0.016 175 0.023 0.033 0.022 0.0160.036 0.016 220 0.023 0.032 0.023 0.017 0.031 0.016 225 0.025 0.0330.025 0.019 0.029 0.018

Referring to Table 5, the laminate of Example 6 exhibited average lossfactors of 0.044 and 0.056 in rounds 1 and 2, respectively, compared toaverage loss factors of 0.020 and 0.014 for Comparative Example E.Hence, Example 6 exhibited 120% and 300% loss factor improvements overComparative Example E for rounds 1 and 2, respectively.

Examples 7 and 8 and Comparative Example F

A damper precursor laminate designated Example 7 was prepared containingsix stacked layers of SLI-272 SMC containing 27 weight percent glass andone viscoelastic layer inserted between the third and fourth SMC layers.Another damper precursor laminate designated Example 8 was preparedcontaining six stacked layers of SLI-272 SMC containing 27 weightpercent glass, and three viscoelastic layers inserted between the thirdand the fourth SMC layers. Both laminates had charge dimensions of 3inches×10 inches.

The laminates of Examples 7 and 8 were compared to a baseline/controllaminate of Comparative Example F, which consisted of a SMC compoundmade from a damper precursor laminate containing six-stacked layers ofSMC as described above in Examples 7 and 8, but with no dampinglayer(s). The laminate of Comparative Example F had charge dimensions of3 inches×10 inches.

After molding, the laminates of Examples 7 and 8 (designated SMC 2 andSMC 3, respectively) and Comparative Example F (designated SMC 1,control) were subjected to two rounds of testing, and exhibited thefollowing loss factors, which are illustrated in graphical form in FIGS.15 and 16, respectively.

TABLE 6 (Loss Factor) for Examples 7 & 8 and Comparative Example FTesting Round 1 Testing Round 2 Temp. Comp. Comp. (° F.) Ex. 7 Ex. 8 Ex.F Ex. 7 Ex. 8 Ex. F 70 0.0244 0.221 0.0187 0.0218 0.0762 0.0144 1000.0244 0.1022 0.0196 0.0234 0.108 0.0159 125 0.0252 0.0742 0.0236 0.02540.1412 0.0190 150 0.0296 0.0618 0.0266 0.0274 0.12 0.0218 175 0.03340.0606 0.0342 0.0312 0.1184 0.0252 220 0.0424 0.074 0.0382 0.0346 0.0960.0320 225 0.0498 0.0728 0.0558 0.0374 0.0942 0.0398

Referring to Table 6, the laminate of Example 8 exhibited average lossfactors of 0.0952 and 0.108 in rounds 1 and 2, respectively, compared toaverage loss factors of 0.0310 and 0.0240 for Comparative Example F.Hence, Example 8 exhibited 207% and 350% loss factor improvements overComparative Example F for rounds 1 and 2, respectively.

The foregoing detailed description of the preferred embodiments of theinvention has been provided for the purpose of explaining the principlesof the invention and its practical application, thereby enabling othersskilled in the art to understand the invention for various embodimentsand with various modifications as are suited to the particular usecontemplated. This description is not intended to be exhaustive or tolimit the invention to the precise embodiments disclosed. Modificationsand equivalents will be apparent to practitioners skilled in this artand are encompassed within the spirit and scope of the appended claims.

1. A damper component for absorbing and dissipating vibration and/ornoise resonation, the damper component comprising: a damper layer havingopposite surfaces and edges, the damper layer comprising aviscoelastomer; and a continuous constraining layer contacting theopposite surfaces and the edges of the damper layer to completely encasethe damper layer, the constraining layer having a greater stiffness andhigher modulus of dynamic shearing elasticity than the damper layer, theconstraining layer comprising a molded polyester sheet molding compoundthat is substantially immiscible with the viscoelastomer to provide adiscrete interface between the constraining layer and the damper layer.2. A damper component according to claim 1, wherein the viscoelastomercomprises a polymeric reaction product of a composition comprising amember selected from the group consisting of (meth)acrylic acid and(meth)acrylate.
 3. A damper component according to claim 1, wherein theviscoelastomer comprises a polyacrylate.
 4. A damper component accordingto claim 1, wherein the viscoelastomer comprises a member selected fromthe group consisting of nitrile rubbers and fluoroelastomers.
 5. Adamper component according to claim 1, wherein the damper layer is freeof fillers.
 6. A damper component according to claim 1, wherein thecontinuous constraining layer further comprises high density fillercomprising a member selected from the group consisting of glass, carbon,aramids, metal, plastics, alumina, silica, silicon, ceramic, andgraphite.
 7. A damper component according to claim 1, wherein thecontinuous constraining layer further comprises chopped fiberglass.
 8. Adamper component according to claim 1, wherein the modulus of dynamicshearing elasticity of the continuous constraining layer is at least twoorders of magnitude greater than that of the viscoelastomer.
 9. A dampercomponent according to claim 1, wherein the modulus of dynamic shearingelasticity of the continuous constraining layer is at least three ordersof magnitude greater than that of the viscoelastomer.
 10. A dampercomponent according to claim 1, wherein the modulus of dynamic shearingelasticity of the continuous constraining layer is at least about500,000 psi.
 11. A damper component according to claim 1, wherein thedamper layer has a thickness in a range of 2.54 microns to 254 microns.12. A damper component according to claim 1, wherein the continuousconstraining layer comprises first and second sheets contacting theopposite surfaces, respectively, and consolidated with one another. 13.A damper component for absorbing and dissipating vibration and/or noiseresonation, the damper component comprising: first and second damperlayers each having opposite first and second surfaces and edges, each ofthe damper layers comprising a viscoelastomer; and a continuousconstraining layer contacting the opposite surfaces and the edges of thedamper layers to completely encase the damper layers, the constraininglayer having a greater stiffness and higher modulus of dynamic shearingelasticity than the damper layers, the constraining layer comprising amolded polyester sheet molding compound that is substantially immisciblewith the viscoelastomer to provide a discrete interface between theconstraining layer and the damper layers.
 14. A damper componentaccording to claim 13, wherein the viscoelastomer comprises a polymericreaction product of a composition comprising a member selected from thegroup consisting of (meth)acrylic acid and (meth)acrylate.
 15. A dampercomponent according to claim 13, wherein the viscoelastomer comprises apolyacrylate.
 16. A damper component according to claim 13, wherein theviscoelastomer comprises a member selected from the group consisting ofnitrile rubbers and fluoroelastomers.
 17. A damper component accordingto claim 13, wherein the damper layers are free of fillers.
 18. A dampercomponent according to claim 13, wherein the continuous constraininglayer further comprises high density filler comprising a member selectedfrom the group consisting of glass, carbon, aramids, metal, plastics,alumina, silica, silicon, ceramic, and graphite.
 19. A damper componentaccording to claim 13, wherein the continuous constraining layer furthercomprises chopped fiberglass.
 20. A damper component according to claim13, wherein the modulus of dynamic shearing elasticity of the continuousconstraining layer is at least two orders of magnitude greater than thatof the viscoelastomer.
 21. A damper component according to claim 13,wherein the modulus of dynamic shearing elasticity of the continuousconstraining layer is at least three orders of magnitude greater thanthat of the viscoelastomer.
 22. A damper component according to claim13, wherein the modulus of dynamic shearing elasticity of the continuousconstraining layer is at least about 500,000 psi.
 23. A damper componentaccording to claim 13, wherein the damper layers each have a thicknessin a range of 2.54 microns to 254 microns.
 24. A damper componentaccording to claim 13, wherein the continuous constraining layercomprises: a first sheet contacting a first surface of the first damperlayer; a second sheet contacting a first surface of the second damperlayer; and a third sheet contacting a second surface of the first damperlayer and further contacting a second surface of the second damperlayer, wherein the first and third sheets are consolidated with oneanother to completely encase the first damper layer, and wherein thesecond and third sheets are consolidated with one another to completelyencase the second damper layer.